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Energy Conversion and Storage; Plasmonics and Optoelectronics
Constructing Unique Cathode Interface by Manipulating Functional Groups of Electrolyte Additive for Graphite/LiNi Co Mn O Cells at High Voltage 0.6
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Bo Liao, Xinliang Hu, Mengqing Xu, Hongying Li, Le Yu, Weizhen Fan, Lidan Xing, Youhao Liao, and Weishan Li J. Phys. Chem. Lett., Just Accepted Manuscript • Publication Date (Web): 29 May 2018 Downloaded from http://pubs.acs.org on May 29, 2018
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The Journal of Physical Chemistry Letters
Constructing Unique Cathode Interface by Manipulating Functional Groups of Electrolyte Additive for Graphite/LiNi0.6Co0.2Mn0.2O2 Cells at High Voltage Bo Liao,† ¶ Xinliang Hu,‡ ¶ Mengqing Xu,*† Hongying Li,† Le Yu,§ Weizhen Fan,§ Lidan Xing,† Youhao Liao,† and Weishan Li *†
†
Engineering Research Center of MTEES (Ministry of Education), Research Center of BMET
(Guangdong Province), Engineering Lab. of OFMHEB (Guangdong Province), Key Laboratory of ETESPG (GHEI), and Innovative Platform for ITBMD (Guangzhou Municipality), School of Chemistry and Environment, South China Normal University, Guangzhou, 510006, China ‡
School of Chemistry and Materials Science, Hubei Engineering University, Xiaogan Hubei 43200,
China §
Guangzhou Tinci Materials Technology Co. Ltd., Guangzhou, 510760, China
ABSTRACT A novel electrolyte additive, 1-(2-Cyanoethyl) pyrrole (CEP), has been investigated to improve electrochemical performance of graphite/LiNi0.6Co0.2Mn0.2O2 cells cycling up to 4.5 V, vs Li/Li+. The 4.5 V cycling results present that after 50 cycles up to 4.5 V capacity retention of the graphite/LiNi0.6Co0.2Mn0.2O2 cell is improved significantly from 27.4 % to 81.5 % when adding 1% CEP to baseline electrolyte (1 M LiPF6 in EC:EMC=1:2, by weight). Ex-situ characterization results support the mechanism of CEP for enhancing electrochemical performance. On the one hand, the 1
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significant enhancement is ascribed to a formed superior cathode interfacial film by preferential oxidation of CEP on the cathode electrode surface suppressing electrolyte decomposition at high voltage. On the other hand, the duo Lewis base functional groups can effectively capture dissociation product PF5 from LiPF6 with the presence of unavoidable trace amount of water or aprotic impurities in the electrolyte. Thus, this mitigates the HF generation which leads to reduction of transition metal dissolution in the electrolyte upon cycling at high voltage. The theoretical modeling suggests that CEP has a mechanism of stabilizing electrolyte via combination of –C≡N: functional group and H2O. The work presented here also shows NMR spectra analysis to prove the capability of CEP reducing HF generation and XPS analysis to observe cathode surface composition. TOC GRAPHICS
KEYWORDS: graphite/LiNi0.6Co0.2Mn0.2O2 cell, 1-(2-cyanoethyl) pyrrole, high voltage, cathode interfacial film, combination with H2O
1. INTRODUCTION Lithium ion batteries (LIBs) have become the focus of tremendous interest in the field of portable electronics, electric vehicles and large-scale energy storage.1,2 Due to the growing battery market for them, customers’ requirement is becoming more competitive in low-cost battery for higher energy 2
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The Journal of Physical Chemistry Letters
density. Consequently, many researchers are focusing on the development of new cathode materials, such as LiNixCoyMn1-x-yO2 (0≤x, y, z
